Abstract
Fire is one of the main factors directly impacting Amazonian forest biomass and dynamics. Because of Amazonia’s large geographical extent, remote sensing techniques are required for comprehensively assessing forest fire impacts at the landscape level. In this context, Light Detection and Ranging (LiDAR) stands out as a technology capable of retrieving direct measurements of vegetation vertical arrangement, which can be directly associated with aboveground biomass. This work aims, for the first time, to quantify post-fire changes in forest canopy height and biomass using airborne LiDAR in western Amazonia. For this, the present study evaluated four areas located in the state of Acre, called Rio Branco, Humaitá, Bonal and Talismã. Rio Branco and Humaitá burned in 2005 and Bonal and Talismã burned in 2010. In these areas, we inventoried a total of 25 plots (0.25 ha each) in 2014. Humaitá and Talismã are located in an open forest with bamboo and Bonal and Rio Branco are located in a dense forest. Our results showed that even ten years after the fire event, there was no complete recovery of the height and biomass of the burned areas (p < 0.05). The percentage difference in height between control and burned sites was 2.23% for Rio Branco, 9.26% for Humaitá, 10.03% for Talismã and 20.25% for Bonal. All burned sites had significantly lower biomass values than control sites. In Rio Branco (ten years after fire), Humaitá (nine years after fire), Bonal (four years after fire) and Talismã (five years after fire) biomass was 6.71%, 13.66%, 17.89% and 22.69% lower than control sites, respectively. The total amount of biomass lost for the studied sites was 16,706.3 Mg, with an average loss of 4176.6 Mg for sites burned in 2005 and 2890 Mg for sites burned in 2010, with an average loss of 3615 Mg. Fire impact associated with tree mortality was clearly detected using LiDAR data up to ten years after the fire event. This study indicates that fire disturbance in the Amazon region can cause persistent above-ground biomass loss and subsequent reduction of forest carbon stocks. Continuous monitoring of burned forests is required for depicting the long-term recovery trajectory of fire-affected Amazonian forests.
Highlights
IntroductionThe Amazon is the world’s largest tropical forest, covering an area of about 5.4 million km2 [1,2]
The Amazon is the world’s largest tropical forest, covering an area of about 5.4 million km2 [1,2].This biome has been hit by two major droughts at the beginning of the 21st century [3]
From field-based quantification of forest fire impacts, airborne Light Detection and Ranging (LiDAR) is capable of surveying larger areas allowing the detection of changes in forest structure, such as canopy gaps, which directly influence forest biomass after the occurrence of disturbances caused by fire
Summary
The Amazon is the world’s largest tropical forest, covering an area of about 5.4 million km2 [1,2] This biome has been hit by two major droughts at the beginning of the 21st century [3]. The second drought, registered in 2010, was attributed to a combination of the El Niño Southern Oscillation (ENSO) with a positive phase of the AMO. These two events caused the intensification of the dry season in the Amazon region, with increased water deficits and reduction of air humidity [5,6,7]. The extended dry and hot weather conditions favored the occurrence of forest fires [8]
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